Use case

A. I want a different animation duration than the one specified by kThemeAnimationDuration.

B. I want to control the properties of themed widgets using an animation controller, and want those to animate immediately and not according to the theme animation duration.

Proposal

1. Add themeAnimationDuration to MaterialApp which is then passed to the created AnimatedTheme.

2. Allow themeAnimationDuration to be overridden or ignored by some mechanism for specific widgets.

It's intuitive that wrapping a widget in AnimatedTheme(data: Theme.of(context), duration: const Duration()) would change the theming animation duration of the widget, but it does not.